The present invention relates to an internal combustion engine fuel injection system and, more particularly, to a fuel injection system having a laminated fuel rail made of composite materials with integral pressure damping.
Modern automotive fuel systems typically employ fuel injectors that control the flow of fuel to each of the engine""s cylinders. Fuel injected engines require a high-pressure fuel feed upstream of the fuel injector that produce system pressures in the range of 300-450 kPa. It is most desirable for the flow of fuel to the cylinders to be carefully controlled for optimal fuel economy and performance, and to minimize emissions from the combusted fuel. Fuel enleanment to the cylinders and cylinder-to-cylinder maldistribution can occur when fuel flow is not carefully controlled. Fuel enleanment (not enough fuel delivered to the cylinder) occurs when the amplitude of fuel pressure pulsations measured in the fuel rail varies with engine speed. This has the effect of changing the average fuel pressure while the injector is open, thereby changing the fuel flow for the same commanded injector on time. Cylinder-to-cylinder maldistribution (uneven apportionment of fuel between cylinders) occurs when the pressure oscillations at the injectors differ from one cylinder to the next during the injector event under constant engine speed and load. The resulting difference in average fuel pressure during the injector event causes variations in cylinder-to-cylinder fuel delivery. Either of these conditions (enleanment or maldistribution) can cause higher emission levels, rough engine operation and a loss in fuel economy.
A typical fuel injection system incorporates a plurality of injectors for delivery of fuel to the inlet ports of the engine. The injectors are mounted in a fuel rail that not only delivers fuel under high pressure to the injectors, but positions each injector in close proximity to either an associated intake manifold runner or its associated intake valve. Most fuel injected engines use electromagnetic fuel injectors which deliver the fuel in metered pulses that are timed to provide the amount of fuel needed for the specific engine operating conditions. Each injector is programmed to pulse or open every other revolution of the engine crankshaft. During an injector opening event, the measured fuel pressure in the fuel rail can instantaneously drop by more than 30 kPa, then increase by more than 50 kPa after the injector closes.
For a typical four cylinder engine operating at 2000 RPMs, the combined injectors pulse at a rate of 66 pulses per second. In such injector-based systems, these pulses cause high frequency pressure waves of significant amplitude to propagate through the fuel rail(s) which, in turn, cause fuel delivery to be compromised as described above and/or fuel line vibration and noise known as xe2x80x9cline hammerxe2x80x9d to occur. Fuel line hammer occurs when the pressure pulsations excite a fuel line or other connected hardware causing it to move or vibrate. The vibrations can be amplified and transmitted into the passenger compartment by body panels or other structural members of the vehicle. The resulting noise, often heard as a xe2x80x9ctickingxe2x80x9d sound, can be mistaken for lifter or injector noise which may be perceived as poor engine quality. Therefore, a damping system is needed to reduce the pressure pulses and vibrations that occur.
Early fuel injection systems were of the fully recirculating type with a high pressure pump in the tank, a spring diaphragm fuel pressure regulator mounted at the fuel rail and a fuel return line running from the rail back to the tank. In this type of system fuel is pumped from the fuel tank to the fuel rail. Excess fuel not injected by an injector is xe2x80x9cbypassedxe2x80x9d back to the fuel tank via the return line. The pressure regulator controls the fuel pressure by varying the flow orifice size between operating pressure in the rail and the low-pressure return line. A side benefit of this type of architecture is that the regulator also provides compliance or damping to the fuel system. In most recirculating systems the regulator is the only component needed to absorb the pressure pulsations found in the system. The negative aspect of a recirculating system is that the return fuel carries heat and fuel vapors back to the fuel tank that can be detrimental to the control of evaporative emissions.
To reduce the transfer of undesirable heat and vapor back to the fuel tank some auto manufacturers have relocated the regulator from the fuel rail to the fuel tank and eliminated the return fuel line. In these types of systems, known as xe2x80x9cdemandxe2x80x9d or xe2x80x9creturnlessxe2x80x9d fuel systems, only the fuel required for engine operation is sent forward from the fuel tank. This effectively eliminates the heat and vapor source from the returning fuel. However, with the regulator in the tank, the beneficial effect of damping out pressure pulsations in the fuel rail is lost. To replace the lost damping in returnless fuel systems, dedicated dampers have been added to or near the fuel rail.
One such pressure-damping device is a spring diaphragm, similar to a regulator, attached to the fuel rail or the fuel supply line. The spring diaphragm operates to reduce pressure pulsations which can cause fuel metering error and audible operating noise produced by the injector pressure pulsations. One acknowledged problem with the spring diaphragm is that it provides only point damping and can lose function at low temperatures. Other problems associated with the use of the spring diaphragm are that it complicates the rail or fuel line, adds more joints susceptible to leakage, can permeate hydrocarbons through the diaphragm, necessitates additional hardware cost, and in many cases does not provide adequate damping.
Another device known in the art is an internal rail damper such as that disclosed in U.S. Pat. No. 5,617,827 (Eshleman et al.). Two shell halves are welded together to form a damper having a sealed airspace filled with trapped air disposed between two compliant sidewalls. The shell material must be hermetically sealed and impervious to gasoline. These shells or volumes have relatively large flat or nearly flat sides that flex in response to rapid pressure spikes in the fuel system. The flexing absorbs the energy of the pressure spikes and reduces the wave speed of the resultant pressure wave thereby reducing the amplitude of the pressure spikes during injector firing events. The internal rail damper needs to be positioned in the fuel rail so as to not adversely affect the flow of fuel to the associated injectors. Although internal dampers have excellent damping properties, a known disadvantage is that it requires the use of end supports to properly position the dampers. These support structures are often difficult and expensive to make due to the intricate slots, grooves and keys required to receive the damper and maintain proper positioning. Also, the fuel rail itself must be specially designed to accommodate the support structures and damper. This may lead to larger fuel rails than are otherwise needed. Other disadvantages include additional assembly time and the further expense of rail end plugs and o-rings.
U.S. Pat. No. 4,660,524 (Bertsch et al.) discloses a metal fuel rail having flat, flexible walls. The flexing fuel rail is provided with large flat surfaces, designed to flex in response to rapid pressure spikes in the fuel system. As pressure pulses occur, the elastic walls function to dampen the pressure pulsations. Flexing fuel rails as disclosed in Bertsch et al. are generally triangular or rectangular in cross section and include long flat sections in one or two side walls of the structure that react to one frequency of pressure pulsation. A rigid wall section to which the mounting hardware and injectors are necessarily affixed accompanies the flexing wall. The fuel rail disclosed in Bertsch et al. limits the rail""s cross section expansion volume. Moreover, because of its welded metal construction, the expansion frequency of the rail cannot be readily tuned to optimize absorption of pressure spikes and to minimize vibration. In addition, the disclosed stainless steel construction is expensive to manufacture. Stainless steel parts require additional processing steps such as stamping, sub-welding, brazing, metal finishing, pasting and processing in a furnace.
In view of the current state of the prior art technology, there exists a need for a molded composite fuel rail formed in an open cross sectional shape having at least one flexible wall whereon stiffener features can be molded to readily tune the absorption characteristics of the fuel rail as needed. Moreover, what is needed is a composite fuel rail that can be molded in laminated layers wherein materials can be selected to add toughness to the design and resistance to alcohol based fuels, and to provide a barrier to keep fuel vapors from permeating through the fuel rail walls.
The present invention generally includes a composite fuel rail with integral damping provided by large flat sections, molded into the rail conduit, that flex in response to pressure pulsations. As an alternate embodiment, the composite fuel rail can be of a laminate construction of different polymer compounds to provide impact resistance, chemical resistance and a permeation barrier as needed for a particular application. Notwithstanding the ability of the composite material to better absorb noise energy as compared to a metal fabricated rail, the present invention also permits molded ribs to be strategically placed along the outer surface of the rail to tune the rail to a particular engine application.
The invention in its broadest aspect comprises an apparatus composite fuel rail with integral damping.
A general aspect of the present invention is to provide a co-injected composite laminate structure that includes impact resistance, chemical resistance and a permeation barrier.
Another aspect of the present invention is to provide a fuel rail with large elastic flat sections molded into the conduit that dampen pressure pulsations with a rigid strengthening rib on which the supports and injector ports are disposed.
Still another aspect of the present invention is to provide a fuel rail that can be tuned to multiple frequencies so that the rail cannot be excited by one frequency.
Still a further aspect the present invention is to provide a fuel rail that reduces audible noise and line hammer without having to add an external dampening system.
These and aspects, features and advantages of the present invention will become readily apparent to those having ordinary skill in the art upon a reading of the following detailed description in view of the appended claims and drawings.